PSA 2014_XI_Q7. Trout are bred in a tank as fish for restaurants. Twenty trout are caught and each is tagged through the tail then released back into the tank. A week later, thirty trout are caught and it is found that two of them have a tail tag.
Based on this evidence alone, what estimate can be made of the total number of trout in the tank ?
Ans: Out of thirty trouts randomly picked, two are found to be having the tail tag. Going by the probability (2/30), the next 30 trouts caught would have 2 with tags and so on. To accomodate 20 tagged trouts the total number of trouts in the tank could be 30*10 or 300. [Linear extrapolation]. Option 2.